Networks of devices capable of measurement, computation and control have been widely deployed for many years. Increasingly, customers deploying such networks expect effortless integration and improved functionality over previous systems. Wired networks are cumbersome in many applications, in some cases impractical or impossible to deploy, and represent a major expense upon deployment. Wired networks are also generally rigid, and the modifications to this infrastructure can be expensive and usually represent an interruption of services and/or a disruption of normal activities.
Alternatively, wireless systems are increasingly being deployed for certain applications. However, some wireless systems, such as those based on optical links, can be unreliable and inconvenient because they need line of sight between transceivers. Other types of wireless systems have other drawbacks, for example Wi-Fi and Bluetooth networks typically use too much power for battery powered applications, and systems based on cellular telephone infrastructure can be very expensive to deploy.
Wireless sensor networks are a new class of systems that address some of the limitations discussed above. In wireless sensor networks, distributed sensors communicate with each other and with host systems to monitor and control a wide variety of devices. Typically, a wireless sensor network is made of numerous small independent sensor nodes. The sensor nodes can be self-contained units consisting of a radio, sensors, and some on-board computing power. The nodes can be organized in networks on a variety of topologies and using a specific communication protocol.
Wireless sensor networks enable the interconnection of points of interest with added intelligence, enabling measurements, control and communications. The potential applications of short range, low data rate wireless sensors are large. Recent advances of semiconductor integration to create near complete systems on silicon is leading to what is known as ‘pervasive computing’ where small, smart and inexpensive devices capable of sensing, communicating, computing and control are found everywhere.
However, wireless sensor networks have not yet been widely deployed partially due to the complexity in hardware and software in such systems, which translates to high cost, large size, and large power requirements. In the case of battery powered units, power requirements often limit the applicability due to short battery life. In some circumstances, wireless sensor networks are limited by the use of standardized communication protocols. In many applications, implementers of wireless sensor networks do not to want standardized communication protocols, because they want to protect their applications, defend their customers against competitors, have a need for more capabilities than what the standard provides, want a lower cost than a standard protocol would require, and/or to want to improve the confidentiality of data. Also, standard protocols tend to be more complex (to include as many applications as possible) thus making them require more resources and higher costs, with lower potential for optimizations. Another disadvantage of standard protocols is that they provide no competitive advantage to end customers since their competitors can then easily add the same functionality.
Another reason resource constrained reactive systems such as the nodes used in wireless sensor networks have not been widely deployed is the lack of efficient, small footprint real-time operating systems for use in such systems. Accordingly, the need exists for an improved system upon which to deploy wireless sensor networks that don't suffer from the limitations described above. In particular, there is a need for efficient real-time operating systems to run on the wireless nodes that can be implemented in a small amount of memory.